Various thermal image transfer methods have been conventionally known. One of the thermal image transfer methods heretofore proposed is such that a polyester film carrying an image printed thereon with a sublimation dye recording agent is used as a thermal transfer sheet and the image on the thermal transfer sheet is thermally transferred onto an image receptor surface by heat and pressure. The term "image receptor surface" is herein meant by a surface or layer of an image receptor to which an image of a sublimation dye recording agent is thermally transferred for formation of the image therein. The image receptor surface is provided on a base to ensure effective thermal image transfer. Therefore, the image receptor surface should have a good dye affinity and dye fixability.
The prior art image receptor surface only serves to fix the dye transferred thereto, but does not offer any aesthetic effects to an article on which the image is formed. In this connection, there has been a demand for a thermal image transfer method which offers aesthetic effects by employing an image receptor surface. Such a demand can be satisfied, for example, by providing an image receptor surface which is adapted to conceal an image (including an illustration and letters) thermally transferred thereto at a temperature out of a predetermined temperature range and turn colorless to make the concealed image visible at a temperature within the predetermined temperature range. More specifically, such an image receptor surface is formed on a surface of a base such as a mug, and an image including unique pictorial and textual messages desired to be sent to a specific person is thermally transferred to the image receptor surface. At this time, the image formed in the image receptor surface is latent but, when the person pours hot water into the mug, the latent image is made visible so that the person receives the unique pictorial and textual messages.